JP6228619B2 - Demineralized and freshwater remineralized by adding calcium carbonate solution to soft water - Google Patents

Description

  The present invention relates to the field of water treatment, and more particularly to methods of water remineralization and the use of calcium carbonate in such methods.

  Drinking water is running short. Even in water-rich countries, not all water sources and reservoirs are suitable for drinking water production, and many of today's water sources are threatened by dramatic degradation of water quality. The water used for drinking purposes was initially primarily surface water and groundwater. However, the treatment of seawater, saltwater, brackish water, wastewater and contaminated effluent is becoming more important for environmental and economic reasons.

  Several methods are known for recovering water from seawater or brackish water for drinking use, which are of considerable importance for dry areas, coastal areas and sea islands, such as distillation, electrolysis and osmosis or reverse osmosis methods. Is included. The water obtained by such a method has a very low hardness due to the lack of pH buffer salts, has a low pH value, and therefore tends to be highly reactive, and if not treated, conventional water Serious corrosion problems can occur during transportation in the pipeline. In addition, untreated demineralized water cannot be used directly as a drinking water source. In order to prevent dissolution of undesirable substances in the pipeline system, to avoid corrosion of waterworks, such as pipes and valves, and to improve the mouthfeel of water, re-adding minerals to water is necessary.

  Conventional methods mainly used for water remineralization are lime dissolution of carbon dioxide and limestone bed filtration. Other less common remineralization methods include, for example, the addition of hydrated lime and disodium carbonate, the addition of calcium sulfate and sodium bicarbonate, or the addition of dichlorocalcium and sodium bicarbonate.

The lime method involves treatment with CO ₂ acidified water and involves the following reactions:
Ca (OH) ₂ + 2CO ₂ → Ca ²⁺ + 2HCO ₃ ⁻

As inferred from the above reaction scheme, 2 equivalents of CO ₂ are required to convert 1 equivalent of Ca (OH) ₂ to Ca ²⁺ and bicarbonate for remineralization. This method relies on the addition of 2 equivalents of CO ₂ to convert alkaline hydroxide ions to the buffer species HCO ₃ . In water remineralization, 0.1 to 0.2% by weight of a calcium dihydroxide saturated solution commonly referred to as lime water, based on the total weight, is prepared from lime milk (usually at most 5% by weight). Therefore, a saturator to produce lime milk lime water must be used, and a large amount of lime water is required to achieve the target level of remineralization. A further disadvantage of this scheme is that hydrated lime is corrosive and requires proper handling and specific equipment. In addition, if the addition of hydrated lime to soft water is not well controlled, undesirable pH changes may be caused due to the lack of lime buffering properties.

The method of limestone bed filtration includes passing soft water through a granular limestone bed to dissolve calcium carbonate in the water stream. By contacting the CO ₂ acidified water limestone:
CaCO ₃ + CO ₂ + H ₂ O → Ca ²⁺ + 2HCO ₃ ⁻
According to this, water is mineralized.

Unlike the lime method, only one equivalent of CO ₂ is stoichiometrically required to convert one equivalent of CaCO ₃ to Ca ²⁺ and bicarbonate for remineralization. Moreover, limestone is not corrosive and large changes in pH are prevented due to the buffering properties of CaCO ₃ .

One further advantage of using calcium carbonate compared to lime is that the carbon dioxide footprint of calcium carbonate is very low. 75 kg of CO ₂ is released to produce 1 ton of calcium carbonate, whereas 750 kg of CO ₂ is released to produce 1 ton of lime. Thus, the use of calcium carbonate instead of lime provides some environmental benefits.

  However, the dissolution rate of granular calcium carbonate is very low and this method requires a filter. This creates a fairly large footprint for this filter and requires a large plant surface area for the limestone bed filtration system.

  Remineralization of water using lime milk or lime slurry is described in US 7,374,694 and EP 0520826. US 5,914,046 describes a method for reducing acidity in effluent effluents using pulsed limestone beds.

US Pat. No. 7,374,694 European Patent No. 0520826 US Pat. No. 5,914,046

  Thus, in view of the shortcomings of known methods for water remineralization, the object of the present invention is to provide an alternative or improved method for water remineralization.

  Another object of the present invention is a water remineralization method that does not require corrosive compounds, thus avoiding the risk of deposition, eliminates the need for corrosion resistant equipment, and provides a safe environment for people working in the plant. Is to provide. It would also be desirable to provide a method that is environmentally friendly and requires a small amount of carbon dioxide when compared to today's water remineralization by the lime method.

  Another object of the present invention is to provide a method for remineralizing water in which the amount of mineral can be adjusted to the required amount.

  Another object of the present invention is to provide a method of remineralization using limestone that allows the use of smaller remineralization units, or a smaller amount of remineralization compound compared to, for example, the lime method. It is to provide a remineralization method that can be used. It would also be desirable to provide a method that can be operated with a smaller plant area than the method of limestone bed filtration.

  The applicant knows as a solution an unpublished European patent application 10172771.7 which describes a method of demineralized and freshwater remineralization by injecting a finely divided calcium carbonate slurry. However, the above and other objects include: (a) providing feed water; (b) providing an aqueous solution of calcium carbonate, the solution comprising dissolved calcium carbonate and a reactive species thereof; and (c) This is solved by providing a water remineralization method comprising combining the feed water of step (a) and the aqueous solution of calcium carbonate of step (b).

  According to another aspect of the present invention, there is provided the use of an aqueous solution of calcium carbonate containing dissolved calcium carbonate and its reactive species for remineralization of water.

1 shows a scheme of an apparatus that can be used to perform the method of the present invention. 3 illustrates another embodiment of the present invention.

  Advantageous embodiments of the invention are defined in the corresponding dependent claims.

  According to one embodiment, the concentration of calcium carbonate in the solution is 0.1 to 1 g / L, preferably 0.3 to 0.8 g / L, more preferably 0.5 to 0, based on the total weight of the solution. 0.7 g / L.

According to another embodiment, the calcium carbonate used in the preparation of the aqueous solution of calcium carbonate in step b) is 0.1 to 100 μm, 0.5 to 50 μm, 1 to 15 μm, preferably 2 to 10 μm, most preferably has a weight median particle size _{d 50} of 5μm from 3 or calcium carbonate is 50μm from 1, of 20μm from 2, preferably from 15μm to 5, most preferably from 8 12 [mu] m of the weight median particle size _{d 50,} Have The calcium carbonate particles can be obtained by friction-based techniques such as milling or grinding under either wet or dry conditions. However, any other suitable method such as sedimentation, rapid expansion of supercritical solutions, spray drying, classification or fractionation of naturally occurring sand or mud, water filtration, sol-gel method, spray reaction synthesis, flame It is also possible to produce calcium carbonate particles by synthesis or liquid foam synthesis.

According to a preferred embodiment of the present invention, the aqueous solution of calcium carbonate of step b) is:
A) Prepare an aqueous suspension of calcium carbonate in the first step and in the second step: (i) any of the carbon dioxide generating compound, (ii) the carbon dioxide generating compound and acid, or (iii) any of the acids B) In the first step: (i) preparation of a solution of a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and either an acid or (iii) a calcium carbonate And then in a second step, introducing either dry form or suspension of calcium carbonate into water, or C) a suspension of calcium carbonate and (i It is prepared by one of the steps of introducing a) a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and either an acid or (iii) an acid.

  For the purposes of the present invention, the term “carbon dioxide generating compound” refers to gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide, a gas containing carbon dioxide, ie a mixture of at least one gas and carbon dioxide, and Includes compounds that release carbon dioxide upon heat or chemical treatment. Preferably, the carbon dioxide generating compound is a gaseous mixture of carbon dioxide and other gases, such as carbon dioxide containing flue gas discharged from an industrial process such as a combustion process or a calcination process, or the carbon dioxide generating compound is a gas Carbon dioxide. When using a gaseous mixture of carbon dioxide and other gases, the carbon dioxide is now present in the range of 8 to about 99% by volume, preferably in the range of 10 to 25% by volume, for example 20% by volume.

  The acid used in the present invention is preferably an acid selected from the group consisting of sulfuric acid, hydrochloric acid, sulfurous acid and phosphoric acid, preferably sulfuric acid or phosphoric acid.

  According to yet another embodiment, the calcium carbonate is 0.02 to 2.5 wt%, 0.05 to 1.5 wt%, or 0.1 to 0.6 wt%, based on the total weight of calcium carbonate. % HCl insoluble content. According to yet another embodiment, the calcium carbonate is ground calcium carbonate, modified calcium carbonate or precipitated calcium carbonate or a mixture thereof.

  According to one embodiment, the solution of step b) is oxidized with minerals containing magnesium, potassium or sodium, preferably magnesium carbonate, calcium carbonate, such as dolomite limestone, calcareous dolomite, dolomite or semi-calcined dolomite, calcined dolomite, etc. Further included is magnesium, magnesium sulfate, potassium bicarbonate or sodium bicarbonate.

  According to another embodiment, the solution of step b) is freshly prepared before use in step b). According to another embodiment, the time period from the preparation of the solution of step b) to the combined water of step a) and the solution of step b) in step c) is less than 48 hours, less than 24 hours, less than 12 hours, Less than 5 hours, less than 2 hours or less than 1 hour. According to yet another embodiment, the solution of step b) meets the microbiological quality requirements defined by the drinking water national guidelines.

  According to one embodiment, the remineralized water obtained is 15 to 200 mg / L, preferably 30 to 150 mg / L, most preferably 100 to 125 mg / L, or 15 to 100 mg / L, preferably It has a calcium concentration as calcium carbonate of 20 to 80 mg / L, most preferably 40 to 60 mg / L.

According to another embodiment, the resulting remineralized water has a magnesium concentration of 5 to 25 mg / L, preferably 5 to 15 mg / L, most preferably 8 to 12 mg / L. According to yet another embodiment, the remineralized water has a turbidity value below 5.0 NTU, below 1.0 NTU, below 0.5 NTU or below 0.3 NTU. According to another embodiment, the remineralized water has a Langeria saturation index of -1 to 2, preferably -0.5 to 0.5, most preferably -0.2 to 0.2. According to another embodiment, the remineralized water has a silt density index SDI ₁₅ of less than 5, preferably less than 4, and most preferably less than 3. According to yet another embodiment, the remineralized water has a membrane fouling index MFI _0.45 of less than 4, preferably less than 2.5, most preferably less than 2.

  According to one embodiment, the feed water is demineralized sea water, brackish or salt water, treated waste water or ground water, natural water such as surface water or rainfall.

  According to one embodiment, the remineralized water is blended with the feed water. According to another embodiment, the method further comprises a particle removal step.

According to one embodiment, the method comprises (d) remineralized water selected from the group comprising alkalinity, total hardness, conductivity, calcium concentration, pH, CO ₂ concentration, total dissolved solids and turbidity. Measuring a parameter value of mineralized water; (e) comparing the measured parameter value with a predetermined parameter value; and (f) an amount based on a difference between the measured parameter value and the predetermined parameter value. The method further includes providing calcium carbonate. According to another embodiment, the predetermined parameter value is a pH value, which is from 5.5 to 9, preferably from 7 to 8.5.

  According to one embodiment, micronized calcium carbonate is used for water remineralization, which can be used for recreational water such as drinking water, swimming pool water, industrial water for processing applications, irrigation water or belts. Selected from water for aquifer or well irrigation.

“Dissolved calcium carbonate and reactive species” means, in the sense of the present invention, the following substances and ions: calcium carbonate (CaCO ₃ ), calcium ions (Ca ²⁺ ), depending on the amount of CO ₂ dissolved at equilibrium conditions, It is understood to include bicarbonate ions (HCO ₃ ⁻ ), carbonate ions (CO ₃ ²⁻ ), carbonate (H ₂ CO ₃ ) and dissolved CO ₂ .

The term “alkalinity (TAC)” as used in the present invention is a measure of the ability of a solution to neutralize an acid to the equivalent point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of dissolved base and is defined as mg / L as CaCO ₃ . Alkalinity can be measured by a titrator.

For the purposes of the present invention, the term “calcium concentration” refers to the total calcium content in the solution and is defined in mg / l as Ca ²⁺ or CaCO ₃ . The calcium concentration can be measured by a titrator.

  “Conductivity” is used in the sense of the present invention as an indicator of how much measured water does not contain salt, ions or impurities; the purer the water, the lower the conductivity. The conductivity can be measured by a conductivity meter and is defined in S / m.

  “Grinded calcium carbonate (GCC)” in the sense of the present invention is calcium carbonate obtained from natural sources including marble, chalk or limestone or dolomite. Calcite is an inorganic carbonate and is the most stable polymorph of calcium carbonate. Other polymorphs of calcium carbonate are inorganic aragonite and vaterite. Aragonite changes to calcite at 380 to 470 ° C. and vaterite is still less stable. The ground calcium carbonate is treated, for example, with a cyclone, by wet and / or dry milling, sieving and / or fractionation. It is known to those skilled in the art that a defined magnesium concentration can be inherently contained, as in the case where the ground calcium carbonate is calcite limestone.

The term “Langeria saturation index (LSI)” as used in the present invention refers to the tendency of aqueous liquids to be scale-forming or corrosive, with positive LSIs indicating a tendency to scale-forming and negative. This LSI exhibits corrosive properties. Thus, an equilibrium Langerian saturation index, LSI = 0, means that the aqueous liquid is in chemical equilibrium. The LSI calculates as follows:
LSI = pH-pH _s
Where pH is the actual pH value of the aqueous liquid and pH _s is the pH value of the CaCO ₃ saturated aqueous liquid. The pH _s can be estimated as follows:
pH _s = (9.3 + A + B)-(C + D)
Where A is a numerical index of total dissolved solids (TDS) present in the aqueous liquid, B is a numerical index (K) of the temperature of the aqueous liquid, and C is a numerical index of the calcium concentration of the aqueous liquid ( CaCO ₃ mg / l) and D are numerical indicators of the alkalinity in the aqueous liquid (CaCO ₃ mg / l). Parameters A through D are determined using the following equation:
A = (log ₁₀ (TDS) -1) / 10
B = -13.12 × log ₁₀ (T + 273) +34.55
C = log ₁₀ [Ca ²⁺ ] −0.4
D = log ₁₀ (TAC)
Where TDS is the total dissolved solids (mg / l), T is the temperature (° C.), [Ca ²⁺ ] is the calcium concentration of the aqueous liquid (CaCO ₃ mg / l) and TAC is the aqueous liquid Alkalinity (CaCO ₃ mg / l).

The term “silt density index (SDI)” as used in the present invention refers to the amount of particulate matter in the water and correlates with the tendency to reverse osmosis or fouling of nanofiltration systems. The SDI can be calculated from, for example, the clogging rate of a 0.45 μm membrane filter when water is passed at a constant applied water pressure of 208.6 kPa. The SDI ₁₅ value is calculated from the clogging rate of the membrane filter when water is passed for 15 minutes at a constant applied water pressure of 208.6 kPa. Typically, spiral-type reverse osmosis requires less than 5 SDIs and hollow fiber reverse osmosis systems require less than 3 SDIs.

  The term “modified fouling index” as used in the present invention refers to the concentration of suspended matter and is an index more accurate than SDI for predicting the tendency to reverse water osmosis or clog nanofiltration membranes. It is. The scheme that can be used to determine the MFI can be the same as for SDI, except that the volume is recorded every 30 seconds over a 15 minute filtration period. MFI uses a graph as the slope of the linear part of the curve when t / V is plotted against V (t is the time (seconds) to collect volume V (liter)). Can be obtained. An MFI value of less than 1 corresponds to an SDI value of less than about 3 and can be considered low enough to control colloidal and particulate fouling.

When using an ultrafiltration (UF) membrane for MFI measurements, the index is called MFI-UF, as opposed to MFI _0.45 when using a 0.45 μm membrane filter.

  For the purposes of the present invention, the term “micronized” refers to particle sizes in the micrometer range, for example 0.1 to 100 μm. Micronized particles can be friction based techniques such as milling or grinding under either wet or dry conditions. However, any other suitable method such as sedimentation, rapid expansion of supercritical solutions, spray drying, classification or fractionation of naturally occurring sand or mud, water filtration, sol-gel method, spray reaction synthesis, flame It is also possible to produce micronized particles by synthesis or liquid foam synthesis.

Throughout this specification, the “particle size” of the calcium carbonate product is indicated by the particle size distribution. The value d _x represents the diameter where the x wt% diameter of the particle is less than d _x . This means that a value of d ₂₀ means that 20% by weight of all particles are smaller than this value, and a value of d ₇₅ means that 75% by weight of all particles are smaller than this value. Means. For this reason, the value d ₅₀ is the weight median particle size, ie 50% by weight of all the grains is larger or smaller than this particle size. For purposes of the present invention, the particle size is defined as the weight median particle size d ₅₀ unless otherwise indicated. To determine the weight median particle size d ₅₀ value of particles having a d ₅₀ of greater than 0.5 μm, a Sedigraph 5100 device from Micromeritics, USA can be used.

“Precipitated calcium carbonate (PCC)” means, in the sense of the present invention, by sedimentation after the reaction of carbon dioxide and lime in an aqueous environment, or by sedimentation of calcium and carbonate sources in water, or calcium from solution and A synthetic material generally obtained by precipitation of carbonate ions such as CaCl ₂ and Na ₂ CO ₃ . Precipitated calcium carbonate exists in three main crystal forms: calcite, aragonite and vaterite, with each crystal form having many different polymorphs (crystal habits). Calcite is a trigonal plane (S-PCC), rhombohedral (R-PCC), hexagonal columnar crystal, table crystal, colloidal (C-PCC), cubic and columnar tetragonal (P-PCC). And a trigonal crystal structure having a typical crystal habit. Aragonite is an orthorhombic structure with twinning hexagonal columnar crystal habits and various combinations of elongated columnar, curved blades, sharp cones, chisel crystals, branched trees and coral or worm-like shapes .

"Modified calcium carbonate" is in the sense of the present invention there is provided a natural calcium carbonate of one or more acid and and / or an external source is generated in situ with 2.5 following pK _a at 25 ° C. Gaseous CO ₂ and optionally at least one aluminum silicate and / or at least one synthetic silica and / or at least one calcium silicate and / or at least one monovalent salt silicate, eg silicic acid Surface-reacted natural carbonic acid obtained by a method of reacting in the presence of sodium and / or potassium silicate and / or lithium silicate and / or at least one aluminum hydroxide and / or at least one sodium and / or potassium silicate It is calcium. Further details regarding the preparation of surface-reacted natural calcium carbonate are disclosed in WO 00/39222 and US 2004 / 0020410A1, the contents of these references are hereby included in this patent application.

  For the purposes of the present invention, a “slurry” contains insoluble solids and water and optionally further additives and usually contains a large amount of solids and is therefore more viscous than the liquid from which the slurry was formed. Generally, it is dense.

  The term “remineralization” as used in the present invention refers to restoring minerals to water that does not contain any or sufficient amounts of minerals in order to obtain palatable water. Remineralization can be achieved by adding at least calcium carbonate to the treated water. In some cases, additional substances can be mixed or mixed with calcium carbonate and then remineralized, for example for health-related benefits or to allow proper intake of some essential minerals and trace elements. It may be added to water during the process. In accordance with national guidelines on human health and drinking water quality, remineralized products may contain additional minerals containing magnesium, potassium or sodium, such as magnesium carbonate, magnesium sulfate, potassium bicarbonate, sodium bicarbonate or essential trace elements. Other inorganic materials containing can be included.

For purposes of the present invention, a solution of calcium carbonate means a clear solution of calcium carbonate in a solvent in which all or almost all of the CaCO ₃ is dissolved to produce a visually clear solution. The solvent is preferably water.

  The term “total dissolved solids (TDS)” as used in the present invention is the combined content of all inorganic and organic substances in liquid, molecular, ionized or particulate (colloidal sol) suspension form. It is a scale. In general, the operational definition is that the solids must be small enough to remain after filtration through a 2 micron sieve sieve size. Total dissolved solids can be assessed by a conductivity meter and is defined in mg / L.

  “Turbidity” in the sense of the present invention refers to the cloudiness or turbidity of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye. Turbidity measurement is a major test of water quality and can be performed using a turbidimetric meter. The unit of turbidity with a calibrated nephelometer as used in the present invention is defined as a nephelometer turbidity unit (NTU).

  The method of the present invention for remineralizing water comprises (a) providing feed water, (b) providing an aqueous solution of calcium carbonate comprising dissolved calcium carbonate and its reactive species, and (c ) Including the step of combining the feed water of step a) with the aqueous calcium carbonate solution of step b)

  The feed water used in the method of the present invention is obtained from various sources. The feed water treated by the method of the present invention is preferably desalted sea water, brackish water or salt water, treated waste water or natural water such as ground water, surface water or rainfall.

According to one embodiment of the present invention, the feed water can be pretreated. Pretreatment may be necessary, for example, when the feed water is obtained from surface water, ground water or rain water. For example, to achieve drinking water guidelines, it is necessary to treat the water using chemical or physical techniques, for example to remove contaminants such as organics or undesirable inorganics. For example, ozone treatment can be used as the first pretreatment step, followed by solidification, aggregation or decantation as the second treatment step. For example, iron (III) salts such as FeClSO ₄ or FeCl ₃ , or aluminum salts such as AlCl ₃ , Al ₂ (SO ₄ ) ₃ or polyaluminum can be used as flocculants. Agglomerated material can be removed from the feed water by, for example, a sand filter or a multilayer filter. Further water purification methods that can be used for pretreatment of the feed water are described, for example, in EP 1975310, EP 1982759, EP 1974807 or EP 1974806.

  According to another exemplary embodiment of the present invention, seawater or brackish water is first pumped from the sea by open sea sampling or subsurface sampling such as wells, and then physically prior to sieving, sedimentation or sand removal treatment, etc. Get processed. Additional processing steps such as coagulation and agglomeration may be required to reduce potential fouling on the membrane depending on the water quality required. The pretreated seawater or brackish water can then be distilled using, for example, multistage flash, multi-effect distillation or membrane filtration such as ultrafiltration or reverse osmosis to remove particulates and dissolved material.

The aqueous solution of calcium carbonate in step b) is preferably the following steps:
A) Prepare an aqueous suspension of calcium carbonate in the first step and in the second step: (i) any of the carbon dioxide generating compound, (ii) the carbon dioxide generating compound and acid, or (iii) any of the acids B) In the first step: (i) preparation of a solution of a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and either an acid or (iii) a calcium carbonate And then in a second step, introducing calcium carbonate into the water, either in dry form or as a suspension, or C) a suspension of calcium carbonate and Prepared by one of the steps of (i) introducing a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and either an acid or (iii) an acid. .

  The carbon dioxide generating compound used is selected from gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide and a gas containing carbon dioxide, preferably the carbon dioxide generating compound is carbon dioxide and other gaseous gases Or a carbon dioxide-containing flue gas discharged from an industrial process such as a combustion process or a calcination process, or the carbon dioxide generating compound is gaseous carbon dioxide. When using a gaseous mixture of carbon dioxide and other gases, the carbon dioxide is now present in the range of 8 to about 99% by volume, preferably in the range of 10 to 25% by volume, for example 20% by volume.

  Gaseous carbon dioxide can be obtained from the storage tank, and the gaseous carbon dioxide is retained in the liquid phase in the storage tank. Depending on the consumption rate of carbon dioxide and the environment, either a cryogenic tank or a conventional insulated tank can be used. Liquid carbon dioxide can be converted to gaseous carbon dioxide using an air heated vaporizer or an electric or vapor based vaporization system. If necessary, the pressure of the gaseous carbon dioxide can be reduced prior to injection, for example by using a pressure drop valve.

Gaseous carbon dioxide can be injected into the feed water stream at a controlled rate to form a dispersion of carbon dioxide bubbles in the water stream to dissolve the bubbles in the water stream. For example, the dissolution of carbon dioxide in the feed water will depend on the starting CO ₂ concentration in the permeate / distillate, the final target pH value (excess CO ₂ ) and the final target calcium concentration (added CaCO ₃ ), 40-60 mg / This can be facilitated by providing a feed water stream at a flow rate of l.

  According to an exemplary embodiment, carbon dioxide is introduced into a turbulent region of water used to prepare the calcium carbonate solution, where turbulent flow can be generated, for example, by restriction in the pipeline. For example, carbon dioxide can be introduced into the venturi throat located in the pipeline. The narrowing of the cross-sectional area of the pipeline in the venturi throat generates turbulent energy that breaks the carbon dioxide into relatively small bubbles, which promotes the dissolution of the carbon dioxide. According to one embodiment, carbon dioxide is introduced into the water stream under pressure. According to another embodiment of the invention, the dissolution of carbon dioxide in the water used to prepare the calcium carbonate solution is facilitated by a static mixer.

A flow control valve or other means can be used to control the flow of carbon dioxide into the water used to prepare the calcium carbonate solution. For example, a CO ₂ dispensing block and a CO _{2 in-} line measuring device can be used to control the flow rate of CO ₂ . According to one exemplary embodiment of the present invention, CO ₂ is injected using a combined unit comprising a CO ₂ dispensing unit, a static mixer and an in-line CO ₂ measuring device.

Carbon dioxide acidifies the feed water by forming carbonic acid. The amount of carbon dioxide injected into the feed water depends on the amount of carbon dioxide already present in the feed water. The amount of carbon dioxide already present in the feed water then varies with upstream processing of the feed water. For example, feed water desalted by flash evaporation differs from the feed water desalted by reverse osmosis in the amount of carbon dioxide it contains and thus has a different pH. For example, feed water desalted by reverse osmosis may have a pH of about 5.3 and a CO ₂ amount of about 1.5 mg / l.

  Remineralization of feed water is induced by injecting a solution of calcium carbonate containing calcium carbonate and its reactive species into the feed water.

  The solution of calcium carbonate injected into the feed water contains dissolved calcium carbonate. According to one embodiment, the concentration of calcium carbonate in the solution is 15 to 200 mg / L, preferably 30 to 150 mg / L, most preferably 100 to 125 mg / L, or 15 to 100 mg / L, preferably 20 to 80 mg / L. L, most preferably 40 to 60 mg / L.

The calcium carbonate used for the preparation of the aqueous solution of calcium carbonate in step b) has a weight median particle size d ₅₀ in the micrometer range. According to one embodiment, the micronized calcium has a weight median particle size d ₅₀ of 0.1 to 100 μm, 0.5 to 50 μm, 1 to 15 μm, preferably 2 to 10 μm, most preferably 3 to 5 μm. The calcium carbonate has a weight median particle size d ₅₀ of 1 to 50 μm, 2 to 20 μm, preferably 5 to 15 μm, most preferably 8 to 12 μm.

  Examples of suitable calcium carbonate are ground calcium carbonate, modified calcium carbonate or precipitated calcium carbonate or mixtures thereof. Naturally ground calcium carbonate (GCC) can be obtained, for example, from one or more of marble, limestone, chalk and / or dolomite. Precipitated calcium carbonate (PCC) may be characterized by one or more of, for example, aragonite, vaterite and / or calcite mineral crystal forms. Aragonite is usually acicular, whereas vaterite belongs to the hexagonal system. The calcite can form a decentered triangular surface, a prismatic shape, a spherical shape, and a rhombohedral shape. Modified calcium carbonate may be characterized by natural ground or precipitated calcium carbonate with surface and / or internal structural modifications, for example, calcium carbonate is treated or coated with a hydrophobizing surface treatment such as, for example, an aliphatic carboxylic acid or siloxane Can be done. Calcium carbonate can be treated or coated to be cationic or anionic, for example with polyacrylate or polydadomac.

  According to one embodiment of the present invention, the calcium carbonate is ground calcium carbonate (GCC). According to a preferred embodiment, the calcium carbonate is ground calcium carbonate having a particle size of 3 to 5 μm.

  According to another embodiment of the present invention, the calcium carbonate is 0.02 to 2.5 wt%, 0.05 to 1.5 wt%, or 0.1 to 0, based on the total weight of the calcium carbonate. .6 wt% HCl insoluble content. Preferably, the HCl insoluble content of calcium carbonate does not exceed 0.6% by weight, based on the total weight of micronized calcium carbonate. The HCl insoluble content may be an inorganic substance such as quartz, silicate or mica.

  In addition to calcium carbonate, the calcium carbonate solution may further comprise a finely divided inorganic material. According to one embodiment, the calcium carbonate solution comprises micronized magnesium carbonate, calcium carbonate, such as dolomite limestone, calcareous dolomite, dolomite or semi-calcined dolomite; magnesium oxide such as calcined dolomite, magnesium sulfate, potassium hydrogen carbonate, hydrogen carbonate Sodium or other minerals containing essential trace elements can be included.

According to one embodiment of the invention, the calcium carbonate solution is freshly prepared before combining it with the feed water. On-site preparation of a solution of calcium carbonate may be preferred. The reason is that if the calcium carbonate solution is not prepared on site and / or freshly prepared, it may be necessary to add additional agents such as stabilizers or biocides to the calcium carbonate solution for reasons of stabilization. . However, such agents may be undesirable compounds in remineralized water, for example for toxicological reasons, or may inhibit the formation of freely available Ca ²⁺ ions. According to one preferred embodiment of the invention, the period between the preparation of the calcium carbonate solution and the injection of the calcium carbonate solution is short enough to avoid bacterial growth in the calcium carbonate solution. According to one exemplary embodiment, the period between the preparation of the calcium carbonate solution and the injection of the calcium carbonate solution is less than 48 hours, less than 24 hours, less than 12 hours, less than 5 hours, less than 2 hours or 1 hour. Is less than. According to another embodiment of the present invention, the injected solution meets the microbiological quality requirements defined by the national guidelines for drinking water.

  A solution of calcium carbonate can be prepared, for example, using a mixer such as a mechanical stirrer in the case of a solution, or a specific powder-liquid mixing device in the case of a higher concentration solution of calcium carbonate, or using a loop reactor. . According to one embodiment of the present invention, the calcium carbonate solution is prepared using a mixer, which allows the simultaneous mixing and dispensing of the calcium carbonate solution.

The water used to prepare the solution can be, for example, distilled water, feed water or industrial water. According to a preferred embodiment of the invention, the water used to prepare the solution is feed water, for example permeate or distillate obtained from desalting. According to an exemplary embodiment of the present invention, the water used to prepare the calcium carbonate solution is acidified with carbon dioxide. Without being bound by any theory, such a CO ₂ pretreatment of the water used to prepare the calcium carbonate solution increases the dissolution of calcium carbonate in the water and thus the reaction time. It will be shortened.

According to one embodiment, a solution of calcium carbonate comprising dissolved calcium carbonate is injected directly into the feed water stream. For example, a solution of calcium carbonate can be injected at a controlled rate into the feed stream by a pump in communication with a storage container for the solution. Preferably, the calcium carbonate solution can be injected into the feed stream at a rate of 1 to 200 l / m ³ feed water, depending on the solution concentration and the final concentration in the remineralized water. According to another embodiment, a solution of calcium carbonate comprising dissolved calcium carbonate is mixed with feed water in a reaction chamber using a mixer, such as a mechanical mixer. According to another embodiment, the calcium carbonate solution is injected into a tank containing the entire feed water stream.

  According to one embodiment of the present invention, only a portion of the feed water is remineralized by injection of a solution of calcium carbonate, followed by blending the remineralized water with the untreated feed water. In some cases, only a portion of the feed water is remineralized to a calcium carbonate concentration that is high compared to the final target value, and then the remineralized water is blended with the untreated feed water.

  According to another embodiment, a high concentration solution of calcium carbonate or a portion of a high concentration solution of calcium carbonate is filtered, eg, by ultrafiltration, to further reduce the turbidity level of remineralized water.

  For the purposes of the present invention, the term “high concentration solution of calcium carbonate” is to be understood as a solution of calcium carbonate containing the maximum possible amount of calcium carbonate dissolved in the respective solvent. The maximum possible amount of dissolved calcium carbonate can be determined by methods known to those skilled in the art, for example by measuring the hardness by conductivity or titration.

The quality of the remineralized water can be evaluated by, for example, the Langeria saturation index (LSI). According to one embodiment, the remineralized water has a Langeria saturation index of −1 to 2, preferably −0.5 to 0.5, most preferably −0.2 to 0.2. According to another embodiment, the remineralized water has a silt density index SDI ₁₅ of less than 5, preferably less than 4, and most preferably less than 3. According to yet another embodiment, the remineralized water has a membrane fouling index MFI _0.45 of less than 4, preferably less than 2.5, and most preferably less than 2. The evaluation can be performed, for example, by continuously measuring the treated feed water. Depending on the remineralization system, the pH of the process pH may be measured, for example, in a process water stream, in a reaction chamber where a solution of calcium carbonate and feed water are mixed, or in a storage tank of remineralized water. it can. According to one embodiment of the invention, the pH is measured after 30 minutes, 20 minutes, 10 minutes, 5 minutes or 2 minutes after the remineralization step. The measurement of the pH value can be carried out at room temperature, ie about 20 ° C.

According to an exemplary embodiment of the present invention, the amount of calcium carbonate solution injected is controlled by sensing the pH value of the treated feed water. Or or in addition, the amount of injected calcium carbonate is controlled by sensing alkalinity, total hardness, conductivity, calcium concentration, CO ₂ concentration, pH, parameters such as total dissolved solids or turbidity . According to one embodiment, the method of the invention is selected from the group comprising (d) alkalinity, total hardness, conductivity, calcium concentration, pH, CO ₂ concentration, total dissolved solids and turbidity of remineralized water. Measuring the parameter value of the remineralized water, (e) comparing the measured parameter value with a predetermined parameter value, and (f) based on the difference between the measured parameter value and the predetermined parameter value. Providing an additional amount of calcium carbonate.

  According to one embodiment, the predetermined parameter value is a pH value, which is 5.5 to 9, preferably 7 to 8.5.

FIG. 1 shows a scheme of an apparatus that can be used to perform the method of the present invention. In the present embodiment, the supply water flows from the reservoir (1) into the pipeline (2). A further pipe (12) is arranged between the reservoir (1) and the storage tank (9). Pipe (12) has a gas inlet (5) through which carbon dioxide from the carbon dioxide source (4) is injected into the supply water, it is possible to prepare CO ₂ acidified water in a first step. The mixer (8) is connected to the pipe (12) downstream of the reservoir (1). In the mixer (8), a solution of calcium carbonate is prepared on-site by mixing the water obtained from the reservoir (1) and the calcium carbonate obtained from the storage container (7) via the pipe (12). . The storage tank (9) can be connected to the pipe (12). A storage tank (9), if present, is provided after the mixer (8) to store the calcium carbonate solution before introducing it into the feed stream. The inlet (10) is located downstream of the reservoir (1) of the pipeline (2) and a solution of calcium carbonate containing dissolved calcium carbonate exiting the mixer (8) is present in the feed water stream through the inlet (10). If so, it is poured into the storage tank (9). The pH of the remineralized water can be measured at the sample point (11) downstream of the slurry inlet (10). According to one embodiment, the feed water flow rate is between 20000 and 500000 m ³ / day.

FIG. 2 shows another embodiment of the present invention. In this embodiment, the aqueous suspension of calcium carbonate is obtained in the first step from calcium carbonate obtained from the storage container (7) into the feed water obtained from the reservoir (1) and flowing in the pipe (12). It is prepared by introducing. In the second step, carbon dioxide from the carbon dioxide source (4) is combined with the water in the pipe (12) already containing a suspension of calcium carbonate in the mixer (8). Next, in order to obtain a solution of calcium carbonate containing dissolved calcium carbonate, water containing a suspension of calcium carbonate and carbon dioxide are mixed. Through the inlet (10) located in the pipeline (2) downstream of the reservoir (1), a solution of calcium carbonate containing dissolved calcium carbonate from the mixer (8) is then injected into the feed water stream. The pH of the remineralized water can be measured at the sample point (11) downstream of the slurry inlet (10). According to one embodiment, the feed water flow rate is between 20000 and 500000 m ³ / day.

  It should be noted that the storage tank (9) is a non-essential equipment for carrying out the method of the invention. In other words, the storage tank (9) need not be present in embodiments of the present invention. In this case, the calcium carbonate solution is injected directly from the mixer (8) into the feed water stream of the pipeline (2) through the inlet (10).

  The method of the present invention may be used to produce drinking water, recreational water such as swimming pool water, industrial water for processing applications, irrigation water or aquifer or well irrigation water.

According to one embodiment, the concentration of carbon dioxide and calcium carbonate in the remineralized water meets the values required for drinking water quality as defined by national guidelines. According to one embodiment, the remineralized water obtained by the method of the invention is 15 to 200 mg / L as CaCO ₃ , preferably 30 to 150 mg / L, most preferably 40 to 60 mg / L, or preferably It has a calcium concentration of 50 to 150 mg / L as CaCO ₃ , most preferably 100 to 125 mg / L as CaCO ₃ . If the solution contains additional magnesium salts such as magnesium carbonate or magnesium sulfate, the remineralized water obtained by the process of the invention is from 5 to 25 mg / l, preferably from 5 to 15 mg / l and most preferably from 8 It may have a magnesium concentration of 12 mg / l.

  According to one embodiment of the invention, the remineralized water has a turbidity below 5.0 NTU, below 1.0 NTU, below 0.5 NTU or below 0.3 NTU.

According to an exemplary embodiment of the present invention, the remineralized water has an LSI of −0.2 to +0.2, a calcium concentration of 15 to 200 mg / l, a magnesium concentration of 5 to 25 mg / l, and 100 as CaCO _3. It has an alkalinity between 200 mg / l, a pH between 7 and 8.5 and a turbidity lower than 0.5 NTU.

  According to one embodiment of the invention, the particle removal step is performed after remineralization, for example to reduce the turbidity level of remineralized water. According to one embodiment, a sedimentation separation step is performed. For example, feed water and / or remineralized water can be piped into a clarifier or storage tank to further reduce the turbidity level of the water. According to another embodiment, the particles can be removed by decantation. Alternatively, at least a portion of the feed water and / or remineralized water can be filtered, eg, by ultrafiltration, to further reduce the turbidity level of the water.

Measuring method:
BET specific surface area BET specific surface area (also referred to as SSA) was measured according to ISO 9277 using a Tristar II 3020 sold by the company Micrometrics ™.

Particle size distribution of particulate material (mass% of particles with diameter less than X μm) and weight median particle size (d ₅₀ ) (d ₅₀ (μm))
Cedigraph ™ 5100
The weight median particle size and particle size distribution of the particulate material was determined by sedimentation method, ie analysis of sedimentation behavior in a gravitational field. Measurements are made with a Cedigraph ™ 5100 sold by Micrometrics ™.

Methods and apparatus are known to those skilled in the art and are commonly used to determine filler and pigment particle sizes. Samples were prepared by adding an amount of product corresponding to 4 g of anhydrous PCC to 60 ml of a 1 wt% aqueous solution of Na ₄ P ₂ O ₇ . The sample was dispersed with a high speed stirrer for 3 minutes (Polytron PT3000 / 3100 at 15,000 rpm). The sample was then sonicated for 15 minutes using an ultrasonic bath and then added to the cedigraph mixing chamber.

Solid weight of suspended material (wt%)
The solid weight (also called the solid content of the material) was determined by dividing the weight of the solid material by the total weight of the aqueous suspension.

  The weight of the solid material was determined by weighing the solid material obtained by evaporating the aqueous phase of the suspension and drying the resulting material to constant weight.

  The following examples illustrate the preparation of different calcium carbonate solutions at various concentrations, which are related to their physical and chemical properties such as carbonate rock, average particle size, insoluble content. From a series of calcium carbonate products.

  Table 1 below summarizes the different calcium carbonate products used during the remineralization test.

A. Laboratory examples:
Three types of samples were used for this test, Sample A is French lime calcium carbonate, Samples B and C were supplied from the same factory in Australia, but were marble calcium carbonate with different weight median particle sizes .

  Table 2 summarizes the different products used during the remineralization test conducted on a laboratory scale.

  The water used for these remineralization was obtained by reverse osmosis (RO) and was water having the following average quality:

  The carbon dioxide used is commercially available as “Kohlendioxid 3.0” by Pangas AG, Dagmaresen, Switzerland. The purity is ≧ 99.9% by volume.

A. 1 Maximum concentration of dissolved calcium carbonate in solution:
Preparation of Calcium Carbonate Solution The maximum concentration of dissolved calcium carbonate in RO (reverse osmosis) water was examined by mixing with RO water pre-added with CaCO ₃ and carbon dioxide (CO ₂ ). Under CO ₂ acidification conditions, it is expected that CaCO ₃ will dissolve up to 1 g. All laboratory tests were performed with a batch of 1 L of RO water, pre-added with CO ₂ at 1.5 L / min for 30 seconds through a glass nozzle placed in the RO water sample.

Calcium lime carbonate (Sample A) was used for the initial test. Prepare initial concentrations of CaCO ₃ of 0.6, 0.8, 1.0 and 1.2 g / L in CO ₂ acidified RO water, and each water sample having a different CaCO ₃ concentration in a closed bottle. Stir for 5 minutes and then settle for 24 hours. The supernatant of each water sample with a different initial CaCO ₃ concentration was taken and analyzed.

Table 3 shows the different results obtained in the preparation of high concentration CaCO ₃ solutions with CO ₂ acidified water using Sample A at different CaCO ₃ concentrations in RO (reverse osmosis) water.

The maximum alkalinity of the four types of supernatants was 466.8 mg / L as CaCO ₃ . This maximum alkalinity was obtained in a supernatant prepared by adding 1.0 g / L CaCO ₃ to CO ₂ acidified RO water. However, some precipitation could still be observed at the bottom of the flask.

Marble calcium carbonate samples B and C were produced from a single production location, but with different weight median particle sizes. Both products were tested to determine the maximum concentration of dissolved CaCO _{3 in} CO ₂ acidified RO water.

This test was conducted under the same conditions as the previous test. For both Samples B and C, the initial CaCO ₃ concentrations used were 0.5 and 0.7 g / L. The supernatant obtained 24 hours after sedimentation was collected and analyzed.

Table 4 shows the different results obtained with the preparation of different high concentration CaCO ₃ solutions in CO ₂ acidified water using Samples B and C at two different CaCO ₃ concentrations in RO.

As can be seen from Table 4, the addition of 0.7 g / L CaCO ₃ to CO ₂ acidified RO water gives the maximum alkalinity of the four types of supernatants, and the supernatants prepared from Sample B and Sample C , CaCO ₃ reached 529.0 and 516.4 mg / L, respectively. The alkalinity of the supernatant prepared from sample C with an initial concentration of 0.5 g / L was lower than expected. The reason for this is not clear, but is probably due to inaccurate addition. Nevertheless, this is consistent with the lower values observed for conductivity and turbidity. However, some precipitation can be observed at the bottom of the flask.

A. 2 pH change during remineralization with calcium carbonate:
Several remineralization tests were performed by adding marble CaCO ₃ high concentration CaCO ₃ solution (samples B and C) into RO water. By diluting the high-concentration CaCO ₃ solution with RO water, appropriate characteristics of the treated water can be realized.

For the purpose of increasing the alkalinity of 45 mg / L as CaCO _3, the volume of the high concentration CaCO ₃ solution was added to the RO water was calculated according to this alkalinity. This addition corresponds to a dilution factor of 8 to 12 for the initial alkalinity of the CaCO ₃ solution. The RO water used in these remineralization tests had a pH value of 5.32, and the alkalinity was 6.32 mg / L as CaCO ₃ .

Samples were taken after 2 minutes of stirring and the conductivity and turbidity were measured to give values of 107 to 118 μS / cm and 0.4 to 0.6 NTU, respectively. After 10 minutes, the final pH and alkalinity were also measured to obtain a pH value of 6.3 to 6.4 and a final alkalinity of 50 to 53 mg / L as CaCO ₃ , respectively.

Table 5 shows the different results obtained for remineralization of RO water by adding highly concentrated CaCO ₃ solutions of Samples B and C to the RO water (45 mg / L CaCO ₃ addition).

Starting from pH 5.32 of RO water, the addition of CaCO ₃ solution caused a rapid pH change from 6.3 to 6.4, and the pH reached a steady state within a few minutes. The final pH was lower than the target value of 7.0 to 8.5. It is thought that CO ₂ was added in excess during this test.

As a conclusion of the high-concentration CaCO ₃ solution with CO ₂ saturated RO water, the maximum alkalinity is CaCO ₃ for the limestone sample A and the rounded value of 470 mg / L, and CaCO ₃ for the marble samples B and C It was between 520 and 530 mg / L. Remineralization with a high concentration CaCO ₃ solution resulted in a rapid increase in pH and a stable pH was obtained within a few minutes. Starting with 6 mg / L alkaline RO water at pH 5.5 and CaCO ₃ , the final pH is 6.3 to 6.4 for RO water remineralization to 50 mg / L alkaline as CaCO _3. The value of is shown.

B. Pilot scale example:
B. 1 Pilot remineralization unit 1:
Following the initial laboratory scale remineralization test, the pilot test was aimed at testing for the implementation of a larger method. The pilot unit also tested different types of calcium carbonate. The water used was deionized water instead of reverse osmosis water. The carbon dioxide used is commercially available as “Kohlendioxid 3.0” by Pangas AG, Dagmaresen, Switzerland. The purity is ≧ 99.9% by volume.

The pilot unit consisted of a 100 L mixing vessel in which powdered CaCO ₃ and deionized water were mixed at the start of each test. The resulting CaCO ₃ solution was then pumped through the tubular reactor at pressures up to 2 bar. CO ₂ was added at a defined flow rate at the start of the tubular reactor, and then remineralized water was flowed through the tubular reactor to completely dissolve the CaCO ₃ in the water. A sample of high-concentration CaCO ₃ solution was taken at the end point of the pipe, and pH, conductivity, and turbidity were measured.

  The deionized water used in these tests had the following average quality:

B. 1.1 Maximum concentration of dissolved calcium carbonate in solution (Sample A):
The maximum concentration of calcium carbonate in deionized water was also tested in a continuous mode with a pilot unit. The pilot test was performed by adding carbon dioxide (CO ₂ ) to an aqueous suspension of calcium carbonate under acidic conditions. Accordance laboratory tests before, at CO ₂ acidification conditions to obtain a maximum alkalinity to the initial concentration of between 500 and calcium carbonate in deionized water 700 mg / L. In all pilot tests, a solution having an initial concentration of calcium carbonate was mixed with deionized water and pumped through a tubular reactor at an average flow rate of 15 L / hr under a pressure of approximately 2 bar.

In the initial pilot test, calcium calcite (sample A) was used at initial concentrations of 0.5, 0.6, 0.7 g / L of CaCO ₃ in CO ₂ acidified water. The residence time in the tubular reactor is approximately 45 minutes, and when a steady state is reached, the resulting high concentration calcium carbonate solution is collected at the outlet of the tubular reactor to obtain pH, turbidity, conductivity. And analyzed for alkalinity.

Table 6 shows the different results obtained in the preparation of high concentration CaCO ₃ solutions with CO ₂ acidified water using Sample A at different initial CaCO ₃ concentrations in deionized water.

As can be seen from Table 6, the maximum alkalinity (within the addition range used) when using Sample A is obtained by adding 0.7 g / L CaCO ₃ to the CO ₂ acidified feed water, and 458 mg as CaCO ₃ . / L, where the turbidity was 3.03 NTU.

B. 1.2 Different types of calcium carbonate:
To prepare a calcium carbonate high concentration solution, calcium lime calcate (sample A) from France was compared with other calcium carbonate products. Two types of marble calcium carbonate with different weight median particle sizes from two different production plants, namely Sample D, produced at the same plant in Austria but with weight median particle sizes of 3.3 and 8.0 μm, respectively Sample E was tested. Similarly, Sample F and Sample G were produced at the same factory in France but had weight median particle sizes of 4.4 and 10.8 μm, respectively. The main difference between the two production areas is the quality of the starting material, the first factory has a very high insoluble content of 2.0% (samples D and E), the second factory Had a low insoluble content of 0.2% (Samples F and G). Sample H, the last product tested, was a very pure and fine Austrian precipitated calcium carbonate (PCC) product.

  Table 7 summarizes the different calcium carbonate products used during the remineralization test conducted on a pilot scale.

The pilot test was conducted in CO ₂ acidified water with a starting concentration of 0.5 g / L CaCO ₃ for each calcium carbonate product. The residence time in the tubular reactor was the same as in the previous pilot test, ie approximately 45 minutes at a flow rate of 15 L / hour. When steady state was reached, the resulting high concentration calcium carbonate solution was collected at the outlet of the tubular reactor and analyzed for pH, turbidity, conductivity and alkalinity.

Table 8 shows the different results obtained with the preparation of high concentration CaCO ₃ solutions in CO ₂ acidified water containing different calcium carbonates for defined CaCO ₃ concentrations in deionized water.

  As can be seen from Table 8, when a sample is taken at the outlet of the tubular reactor, a high concentration calcium carbonate solution having maximum alkalinity is obtained when a precipitated calcium carbonate (PCC) product (sample H) is used. It was. However, the turbidity measured with this high concentration calcium carbonate solution is not the minimum value obtained in this series of tests. Compared to all marble products (samples D, E, F, G), calcium lime calcate (sample A) showed lower turbidity values. When comparing two products of different particle sizes, such as samples D and E or samples F and G, it was surprisingly found that the higher the average particle size, the lower the turbidity . However, as expected, the smaller the average particle size, the higher the final alkalinity and conductivity.

B. 1.3 Dilution to target remineralization concentration:
In order to meet the target water quality, a high concentration calcium carbonate solution is dissolved with deionized water. In order to reduce the alkalinity to 45 mg / L as CaCO ₃ , the dilution factor was defined according to the initial alkalinity of the high concentration calcium carbonate. The final pH was adjusted to 7.8 with 5 wt% NaOH solution and the final turbidity was measured.

Table 9 shows the different results of remineralized water obtained by adding the high concentration CaCO ₃ solution of Sample A to deionized water (addition of 45 mg / L CaCO ₃ ).

  As can be seen from Table 9, the minimum turbidity level for this remineralization test using high concentrations of calcium carbonate was 0.39 NTU (fractional 0.4 NTU). The remaining tests gave higher turbidity of 0.8 to 1.0 (0.97 and 1.03 rounded values) NTU.

  There is also a need to adjust the content of soluble magnesium compounds in the final potable water to about 10 mg / L Mg, according to the respective WHO guidelines.

Prior to introducing the solution into the tubular reactor, the magnesium salt was mixed with calcium carbonate sample A to attempt to adjust the Mg content in the solution. Although MgSO ₄ was selected as the soluble Mg salt, it is stated that the final level of sulfate in the water should still be within acceptable limits (less than 200 ppm), especially when using treated water for agricultural applications. For the purpose of reducing the alkalinity to 45 mg / L as CaCO ₃ , the dilution factor was also defined according to the initial alkalinity of the high concentration calcium carbonate. The final pH was adjusted to 7.8 with 5 wt% NaOH solution and the final turbidity was measured.

Table 10 shows the different results of remineralized water obtained by adding high concentration CaCO ₃ solution of Sample A and magnesium sulfate to deionized water (addition of 45 mg / L CaCO ₃ ).

  In order to evaluate the characteristics of all potable water, some samples of remineralized water were sent to a water quality control laboratory. For example, remineralized water obtained using only calcium carbonate and showing the lowest turbidity level was obtained from Test Nos. 12 and 15. Remineralized water obtained using a mixture of calcium carbonate and magnesium sulfate and showing the lowest turbidity level was obtained from test number 17. These three samples were sent for analysis to the Carinthian Institute for Food Analysis and Quality Control in Austria, where the water samples meet the stringent Austrian guidelines for drinking water quality and the WHO guidelines for soluble magnesium. It was recognized that

Table 11 shows the drinking water quality of remineralized water obtained by adding the high concentration CaCO ₃ solution of Sample A to deionized water (addition of 45 mg / L CaCO ₃ ).

B. 2 Pilot remineralization unit 2:
After the initial pilot remineralization test, a new series of pilot-scale tests were conducted with a pressure range of 2 to 7 bar, an RO water flow rate between 300 and 400 L / hr, and a CO flow between 1.1 and 5.5 L / min. _This was done in a separate remineralization unit that was operable with ₂ additions. The carbon dioxide used is commercially available as “Kohlendioxid 3.0” by Pangas AG, Dagmaresen, Switzerland. The purity is ≧ 99.9% by volume.

The pilot unit consisted of a 60 L mixing vessel into which powdered CaCO ₃ and RO water were introduced a defined number of times (ie more than once). The resulting CaCO ₃ solution was then pumped through a mixer where CO ₂ was added at a defined flow rate and the high concentration CaCO ₃ solution was passed through a pipe to completely dissolve the CaCO ₃ in water. The residence time in the tubular reactor is approximately 45 minutes, and when a steady state is reached, the resulting high concentration calcium carbonate solution is collected at the outlet of the tubular reactor to obtain pH, turbidity, conductivity. And analyzed for alkalinity.

B. 2.1 Different working pressures:
To test for the effect of pressure on dissolution of calcium carbonate in RO water under acidic conditions with carbon dioxide (CO ₂ ), different working pressures were tested in the above remineralization pilot unit. According to the results from the previous pilot test, an initial concentration of 500 mg / L of calcium carbonate was prepared in RO water and the resulting solution was added with a slight excess of CO ₂ . Pilot tests conducted at different working pressures had a flow rate of 300 L / hr and the pressure was varied between 2 and 7 bar. The calcium carbonate used in these pilot tests was French limestone (Sample A).

Table 12 shows a high concentration CaCO ₃ solution in CO ₂ acidified water using Sample A with a concentration of 0.5 g / L of CaCO ₃ in RO water at a flow rate of 3.3 L / min at different pressures. The different results obtained with the preparation of

These pilot tests showed that higher pressures under these test conditions did not improve the dissolution of CaCO ₃ and resulted in higher turbidity for the higher pressures tested. One of the consequences of using higher pressure is the temperature rise of the CaCO ₃ solution, which is due to the pump. Thus, the remineralized water leaving the pilot unit is hotter, which can have an impact on the solubility of CO _{2 in} the water. In other words, the higher the water temperature, solubility in CO ₂ in water is low. As a result of the reaction scheme below:
CaCO ₃ + CO ₂ + H ₂ O → Ca ²⁺ + 2HCO ₃ ⁻
There is less dissolved CaCO _{3 in} solution, which in turn leads to higher turbidity levels due to the amount of undissolved CaCO ₃ .

B. 2.2 Different CO ₂ flow rates:
It is highly conceivable that the addition of CO ₂ has a great influence on the dissolution rate of CaCO _{3 in} RO water. Therefore, different flow rates of CO ₂ were tested for the preparation of high concentration solutions of CaCO ₃ . All tests were performed using the same protocol as described in previous tests at defined pressures but with different CO ₂ flow rates.

Table 13 shows high concentration CaCO ₃ in CO ₂ acidified water using Sample A with a concentration of 0.5 g / L of CaCO ₃ in RO water at a pressure of 5.5 bar using different CO ₂ flow rates. The different results obtained with the solution preparation are shown.

From the results shown in Table 13, it can be seen that the solubility of CaCO _{3 in} RO water under the test conditions can be improved when the CO ₂ flow rate is increased. This can be derived from an increase in conductivity and a decrease in turbidity at the reaction pipe outlet when the CO ₂ flow rate is increased.

B. 2.3 Residence time:
Tests were also conducted on the residence time assigned to cause dissolution of CaCO ₃ . In this regard, pilot testing was performed using either one or two pipes connected in sequence. This setting doubled the residence time from approximately 45 minutes for one pipe to approximately 90 minutes for two connected pipes, thus allowing the effect of residence time on the resulting turbidity and conductivity to be investigated. .

Table 14, a high concentration CaCO at different residence CO in ₂ flow and pressure defined for time, CO ₂ acidified water using sample A having a concentration of 0.5 g / L of CaCO ₃ in RO water _The different results obtained with the preparation of the _three solutions are shown.

The two sets of tests shown in Table 14 indicate that the residence time has a direct effect on the dissolution of CaCO _{3 in} RO water under both test conditions, ie test numbers 28 and 29 and test numbers 30 and 31. It is clearly shown. It can clearly be seen that the longer the residence time, the lower the turbidity and the higher the respective conductivity.

C. Additional Examples: Marble / limestone The following examples are by addition of CO ₂ to a suspension of calcium carbonate and filtration of the resulting suspension through an ultrafiltration membrane to remove residual insolubles. Figure 2 shows the preparation of a concentrated solution of calcium bicarbonate in reverse osmosis (RO) water.

  Two types of calcium carbonate products are selected according to their physical and chemical properties, namely carbonate rock, average particle size, insoluble content and specific surface area, and the final turbidity of the filtered concentrated calcium bicarbonate solution and It was compared with conductivity.

  Table 15 below summarizes the different calcium carbonate products used during pilot testing for the preparation of calcium bicarbonate solutions.

  The RO water used for these tests has the following average quality:

C. 1 Pilot scale example:
A series of pilot-scale tests were conducted in a reactor system under the following conditions of use:
Pressure: about 2.5 bar, flow rate: about 300 L / hr, CO ₂ addition: 3.3 L / min The carbon dioxide used is commercially available as “Kohlendioxid 3.0” by Pangas AG, Dagmaresen, Switzerland. The purity is ≧ 99.9% by volume.

The reactor system consists of a 60 L mixing tank and has a calcium carbonate initial concentration of 500 to 1000 mg / L (0.05 to 0.1 wt%) in which powdered forms of CaCO ₃ and RO water are defined. Introduced (ie more than once). The starting CaCO ₃ suspension was then pumped through a mixer where CO ₂ was added at a defined flow rate to dissolve the calcium carbonate in RO water according to the following reaction:
CaCO _{3 (s)} + CO _{2 (aq)} + H ₂ O → Ca (HCO ₃ ) _{2 (aq)}
The resulting suspension was passed through a pipe to completely dissolve CaCO ₃ in water. The residence time in the pipe was approximately 40 minutes, and when a steady state was reached, the resulting suspension was collected at the outlet of the pipe and analyzed for conductivity and turbidity.

  The resulting suspension was then pumped through an Inge dizzer P2514-0.5 type ultrafiltration membrane to remove soluble material. Tests were conducted with two different filtration schemes, crossflow and dead-end: the former scheme was that 2/3 of the flow rate was recirculated and 1/3 of the flow rate passed through the membrane, the latter being The entire flow rate is passed through an ultrafiltration membrane.

  The conductivity and turbidity of the filtered calcium bicarbonate solution was also analyzed and compared to the unfiltered resulting suspension that was recycled back to the initial feed calcium carbonate solution and tank.

C. 1.1 Test feed with very pure calcium carbonate (or starting) CaCO ₃ solution in reverse osmosis water with different initial concentrations of calcium carbonate but different stoichiometric excess of CO ₂ and residence time Prepared using A.

  Table 16 shows the use conditions in the cross flow system for the preparation of the calcium bicarbonate solution (sample A) in RO water.

Table 17 shows the different results obtained with the feed CaCO ₃ suspension (sample A) and the resulting unfiltered suspension and unfiltered calcium bicarbonate solution.

The residence time used to prepare the feed CaCO ₃ suspension did not affect the conductivity and turbidity of the filtered calcium bicarbonate solution (Tests 1 and 2). This means that shorter residence times can be used to prepare the calcium bicarbonate solution when ultrafiltration is used for the final removal of the soluble portion. The resulting unfiltered suspension that was recirculated to the tank showed significantly lower turbidity levels than the feed CaCO ₃ suspension and continued to decline as the recirculation continued.

Increasing the initial concentration of the feed CaCO ₃ suspension has been shown to increase the conductivity level of the filtered calcium bicarbonate solution even with a lower CO ₂ excess (Test 3). The very high turbidity level of 200 to 240 NTU of the feed CaCO ₃ suspension in this test did not affect the final turbidity produced after ultrafiltration, for example below 0.8 NTU.

C. 1.2 Test feed CaCO ₃ suspension with calcium carbonate containing high insolubles content has a residence time of 40 minutes, 6 and 3 times the stoichiometric excess of CO ₂ and crossflow or dead-end mode In either case, sample B was prepared using different initial concentrations of calcium carbonate in reverse osmosis water.

  Table 18 shows the use conditions for the preparation of calcium bicarbonate solution in RO water using Sample B.

Table 19 shows the different results obtained with the feed CaCO ₃ suspension and the resulting suspension prepared with Sample B and the filtered calcium bicarbonate solution.

Comparing tests 2 and 4, the high insoluble content of sample B clearly only has an effect on the turbidity of the feed CaCO ₃ suspension, ie for the feed CaCO ₃ suspension prepared with sample A The turbidity was 27 to 32 NTU, and the turbidity was 52 to 61 NTU for the feed CaCO ₃ suspension prepared using Sample B. However, the final conductivity and turbidity of the filtered calcium bicarbonate solution are similar, with either filtered calcium bicarbonate solution having a maximum turbidity level of 0.7 to 0.8 NTU and a conductivity of 695 to 705 μS / cm.

When comparing tests 3 and 5, it is clear that the high insoluble content of sample B has no effect on either turbidity or conductivity of both feed CaCO ₃ suspensions, ie The turbidity level was 200 to 240 NTU and the conductivity level was 870 to 890 μS / cm. This is because there is so much undissolved CaCO ₃ present in both feed suspensions that this probably gives rise to almost all turbidity, and the soluble part derived from the raw material is turbid under these conditions. This is because it has no influence on

  The filtered calcium bicarbonate solution also showed similar final conductivity and turbidity levels, with a maximum turbidity level of 0.7 to 0.8 NTU and conductivity of 870 to 880 μS / cm. These results confirm that the insoluble content of the raw material does not affect the final quality of the calcium bicarbonate solution when using ultrafiltration.

  Finally, the dead-end filtration mode did not show any significant change during the test period of test 5, and similar results were obtained compared to the test using the crossflow filtration mode.

Claims (26)

A method for remineralization of water comprising:
a) providing feed water;
b) providing an aqueous solution of calcium carbonate containing dissolved calcium carbonate and its reactive species; and c) combining the feed water of step a) with the aqueous calcium carbonate solution of step b), Aqueous solution
A) preparing an aqueous suspension of calcium carbonate in a first step, and in a second step: (i) a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and an acid, or (iii) an acid, Introducing into an aqueous suspension of calcium carbonate, or B) in a first step: (i) a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and an acid, or (iii) an acid Introducing either into the water used to prepare the solution of calcium carbonate and then introducing in a second step either dry or suspended calcium carbonate into the water, or C) Of simultaneously introducing a suspension of calcium carbonate and either (i) a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and an acid, or (iii) an acid. One of has been prepared by the steps, and calcium carbonate to be used in the preparation of an aqueous solution of calcium carbonate in step b) has a 100μm weight median particle size d ₅₀ from 0.1, is and remineralization Kamizu A method having a turbidity value lower than 1.0 NTU.   The method of claim 1, wherein the concentration of calcium carbonate in the solution is 0.1 to 1 g / L based on the total weight of the solution.   The method of claim 1, wherein the concentration of calcium carbonate in the solution is from 0.3 to 0.8 g / L based on the total weight of the solution. The method according to any one of claims 1 to 3, calcium carbonate used in the preparation of an aqueous solution of calcium carbonate in step b) has a weight median particle size d ₅₀ of 50μm from 0.5, or The method wherein the calcium carbonate has a weight median particle size d ₅₀ of 1 to 50 μm. The method according to any one of claims 1 to 3, calcium carbonate used in the preparation of an aqueous solution of calcium carbonate in step b) is from 2 has a weight median particle size d ₅₀ of 10 [mu] m, or the carbonate The method wherein the calcium has a weight median particle size d ₅₀ of 5 to 15 μm.   6. The method according to any one of claims 1 to 5, wherein the calcium carbonate is ground calcium carbonate, modified calcium carbonate, precipitated calcium carbonate, or a mixture thereof.   The method according to any one of claims 1 to 6, wherein the remineralized water obtained has a calcium concentration as calcium carbonate of 15 to 200 mg / L.   The method according to any one of claims 1 to 6, wherein the remineralized water obtained has a calcium concentration as calcium carbonate of 30 to 150 mg / L.   9. The method according to any one of claims 1 to 8, wherein the solution of step b) further comprises an inorganic material containing magnesium, potassium or sodium.   9. The method according to any one of claims 1 to 8, wherein the solution of step b) further comprises an inorganic substance containing magnesium carbonate, calcium carbonate, magnesium oxide, magnesium sulfate, potassium bicarbonate, or sodium bicarbonate. Including.   11. A method according to claim 9 or 10, wherein the remineralized water obtained has a magnesium concentration of 5 to 25 mg / L.   11. A method according to claim 9 or 10, wherein the remineralized water obtained has a magnesium concentration of 5 to 15 mg / L.   13. A method according to any of claims 1 to 12, wherein the remineralized water has a Langeria saturation index of -1 to 2.   13. A method according to any of claims 1 to 12, wherein the remineralized water has a Langeria saturation index of -0.5 to 0.5. _15. The method according to any of claims 1 to 14, wherein the remineralized water has a silt density index SDI ₁₅ of less than 5. _15. The method according to any of claims 1 to 14, wherein the remineralized water has a silt density index SDI ₁₅ of less than 4. 17. A method according to any of claims 1 to 16, wherein the remineralized water has a membrane fouling index MFI _0.45 of less than 4. 17. A method according to any of claims 1 to 16, wherein the remineralized water has a membrane fouling index MFI _0.45 of less than 2.5.   19. A method according to any of claims 1 to 18, wherein the feed water is desalted sea water, brackish water or salt water, treated waste water, or natural water.   20. A method according to any preceding claim, wherein the remineralized water is blended with the feed water.   21. The method according to any of claims 1 to 20, further comprising a particle removal step. A method according to any of claims 1 to 21, comprising
d) measuring the parameter values of the remineralized water, the parameters being alkalinity, total hardness, conductivity, calcium concentration, pH, CO ₂ concentration, total dissolved solids, and turbidity of the remineralized water A step selected from the group comprising degrees,
e) comparing the measured parameter value with the predetermined parameter value; and f) providing an injection amount of the calcium carbonate solution based on the difference between the measured value and the predetermined parameter value. .   23. The method according to claim 22, wherein the predetermined parameter value is a pH value, and the pH value is 5.5 to 9.   23. The method according to claim 22, wherein the predetermined parameter value is a pH value and the pH value is 7 to 8.5. Use of an aqueous solution of calcium carbonate for remineralization of water, comprising combining an aqueous solution of water and calcium carbonate,
An aqueous solution of calcium carbonate
A) preparing an aqueous suspension of calcium carbonate in a first step, and in a second step: (i) a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and an acid, or (iii) an acid, Introducing into an aqueous suspension of calcium carbonate, or B) in a first step: (i) a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and an acid, or (iii) an acid Introducing either into the water used to prepare the solution of calcium carbonate and then introducing in a second step either dry or suspended calcium carbonate into the water, or C) Of simultaneously introducing a suspension of calcium carbonate and either (i) a carbon dioxide generating compound, (ii) a carbon dioxide generating compound and an acid, or (iii) an acid. One of has been prepared by the steps, and calcium carbonate to be used in the preparation of an aqueous solution of calcium carbonate has a 100μm weight median particle size d ₅₀ from 0.1, and
Remineralization water, is to have a lower turbidity values than 1.0NUT, used.   26. The use according to claim 25, wherein the remineralized water is selected from potable water, recreational water, industrial water for processing applications, irrigation water, or aquifer or well irrigation water. use.

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